A nose for love – oceanbites

Martin, Rene P., and W. Leo Smith. “First evidence of sexual dimorphism in olfactory organs of deep-sea lanternfishes (Myctophidae).” PeerJ 12 (2024): e17075.

At the risk of understatement, the deep sea is big and dark. In fact, it is extremely dark (no light reaches from the sun) and extremely big (by far the largest habitat on Earth). How do animals find mates in such a place?

Many deep-sea creatures are bioluminescent—that is, they make their own light. This is an important way for animals to communicate and find one another. However, visual signals may only be effective over short distances. Most bioluminescent fish probably don’t make enough light to be seen from far away. Luckily, there is a signal that can travel much further than light underwater: smell.

My, what a big nose you have 

Many animals are sexually dimorphic, meaning that the sexes tend to have different physical traits. In humans, sexual dimorphism is actually quite limited compared to apes and other animals. Human males are slightly larger than females on average, but to a much lesser extent than, say, chimpanzees and gorillas, where males are much larger. Other animals have even more extreme cases of sexual dimorphism: famously, some deep-sea anglerfish have tiny “parasitic” males that attach themselves to the (comparatively enormous) females.

Recently, biologists found another example of sexual dimorphism in deep-sea fish. In some lanternfish, males and females are the same size, but males have bigger noses (or, technically, “olfactory rosettes”). This suggests that the males have a more sensitive sense of smell, which they could use to detect chemical signals (“pheromones”) produced by females.

A light… I mean, a smell in dark places

These lanternfish also have sexually dimorphic bioluminescence. The males have light-producing organs, but the females do not. Therefore, the males might use a multi-sensory dating strategy, using smell to find females from distance and then use bioluminescent courtship to attract the female once they get close.

You’ve probably heard that sharks can smell blood in the water from miles away. This study highlights that fish can use smell to find romance, not just food! In fact, smell affects mating dynamics in lots of animals, even on land. Humans also make pheromones, and these smelly chemicals influence human attraction and mate choice. However, smell is even more important for fish because chemical cues travel far underwater. Long-distance chemical-based communication might be the solution to the problem of finding other fish in vast, dark ocean habitats.

Cover image source: NOAA

I am a PhD student at MIT and the Woods Hole Oceanographic Institution, where I study the evolution and physiology of marine invertebrates. I usually work with zooplankton and sea anemones, and I am especially interested in circadian rhythms of these animals. Outside work, I love to play trumpet, listen to music, and watch hockey.